This invention relates to a method for the manufacture of A.sub.3 B.sub.5 light-emitting diodes (LEDs), especially (Ga,Al)As light-emitting diodes with Te and Zn as doping materials by precipitation of (Ga,Al)As from n- and p-doped Ga,Al,As melts via liquid-phase epitaxy.
Light-emitting diodes are semiconductor diodes with a pn junction which, upon application of a voltage in the forward direction at the pn junction and in its immediate vicinity emit nondirectional incoherent electromagnetic radiation in the infra-red, visible or ultra-violet spectral ranges. As semiconductor material for these light-emitting diodes, III-V compounds are particularly suitable. Light-emitting diodes are suitable for a wide variety of optoelectronic applications. For instance, by means of LEDs electrical energy can be converted into light energy and can thereby be transmitted optically. The light output of light-emitting diodes should be as high as possible.
It is known to precipitate on a GaAs substrate by heteroepitaxy methods, in which two mixed-crystal layers with different Al content and conduction type from two Ga,Al,As melts are deposited in two separate epitaxy steps on a GaAs substrate (See, IEEE Transactions on Electron Devices, Vol. Ed-28, No. 4, April 1981). The several operations required for epitaxy for heterostructures of relatively complicated designs, require several Al-containing Ga- melts and a relatively large amount of technical and technological means. Furthermore, relatively thick Ga,Al,As melts are required to ensure a constant Al content in the mixed-crystal layer with a thickness of, for instance, 20 .mu.m to 30 .mu.m.
A method is also known in which the Al content decreases continuously with increasing layer growth. This method is known by the name "Graded-band-gap method" and is described, for instance, in "Journal of Applied Physics", vol. 48, No. 6, June 1977. The incorporation close to the edge of the band, which is present, for instance, with Te, causes high absorption losses of the light produced at the pn junction, together with low light yield.